Evidence of counteroffers, discussed below, can lead the courts to conclude that the contract has not been fully constituted.Once an offer has been accepted the court will expect the offeror to give the promised consideration. If the offeror fails to do this, the court will deem that a breach has occurred, which would entitle the offeree to be able to sue for that breach. Offers can be revoked before the deadline, although if the other party has already started to perform their part of the bargain, the court will generally refuse to allow the offeror to revoke the offer. This might occur in a situation where the offeror is offering a reward for the finding of a lost item.Where acceptance of an offer is communicated by post, the court will generally hold the acceptance as being valid from the date that the acceptance was posted on. In Adams v Lindsell, the court held that“Where the circumstances are such that it must have been within the contemplation of the parties that, according to the ordinary usages of mankind, the post might be used as a means of communicating the acceptance of an offer, the acceptance is complete as soon as it is posted”.From this case, it has become an accepted principle that acceptance will be regarded as valid from the date on which the acceptance was posted. This will generally apply even if the offeror does not receive the communication until a considerable time after the deadline date.An invitation to treat occurs with items advertised in brochures, on the internet, in newspapers and in shop windows. The legal perspective is based on the notion that the seller is inviting the customer to make them an offer to buy the goods. With goods displayed in a shop, the shopkeeper is inviting the customer to offer to buy the items. Once the item is presented at the till for purchase, the seller is entitled to either sell the advertised item or reject the offer. The same principle applies to items advertised in a newspaper or brochure, or on the internet.